Apparatus for the fabrication of tubes by wall thinning in tubular blanks



United States Patent 6,881/65 US. CI. 72-57 Int. Cl. B21d 39/08, 28/18, 22/10 6 Claims ABSTRACT OF THE DISCLOSURE Apparatus for the production of a thin walled tube by forcing a plug through the bore of a tubular blank, the plug being of larger diameter than the bore of the tubular blank comprising a pressure resistant containing vessel corresponding in internal diameter to the external diameter of the tubular blank, means for generating pressure in a primary hydraulic liquid in the bore of the tubular blank on one side of the plug when entered into the bore of the tubular blank and means for generating a lower pressure in a secondary hydraulic liquid on the other side of the plug in the bore of the tubular blank.

This invention relates to the formation of tubular articles and is particularly but not exclusively concerned with the formation of thin walled tubes in brittle materials.

Known tube fabrication processes, such as tube draw ing, cannot be satisfactorily applied to the production of thin walled tubing in brittle materials because the action of drawing imposes tensile stresses on the material. Brittle materials are of low strength under tensile stressing and the application of tube drawing methods to the production of tubing in such materials usually results in failure of the material by cracking or complete fracture during fabrication.

Tubes can be produced from brittle materials by swaging down of a tubular blank on a mandrel but this operation is time consuming and complications arise in withdrawal of the mandrel from the tubular product after fabrication.

According to the invention a method for the production of a thin walled tube by wall thinning of a tubular blank comprises forcing a plug, of larger diameter than the bore of the tubular blank, through the tubular blank, whilst the tubular blank is held in a close fitting containing vessel resistant to internal pressure, the plug being forced through the bore of the tubular blank by the application of a primary hydraulic liquid under pressure on one side of the plug in the bore of the tubular blank, a secondary hydraulic liquid at a lower pressure being applied on the other side of the plug in the bore of the tubular blank.

With the application of hydraulic liquid under pressure in the bore of the tubular blank on both sides of the plug, tensile stresses in the material are eliminated or so reduced that brittle materials can be worked by means of the method.

In apparatus for carrying out the method of the invention a pressure resistant containing vessel is provided having an internal diameter corresponding to the external diameter of the tubular blank, means being provided for generating pressure in the primary hydraulic liquid applied in the bore of the tubular blank on the one side of the plug and means being provided for generating a lower pressure in the secondary hydraulic liquid applied on the other side of the plug in the bore of the tubular blank.

3,427,843 Patented Feb. 18, 1969 In a preferred form of apparatus the containing vessel is of cylindrical tubular form comprising longitudinal segments having radial mating faces, the segments being contained within a thin outer sheath, means being provided sealing the end faces of the segments against ingress of hydraulic liquid between the radial mating faces of the segments.

In this form of containing vessel, hydraulic liquid under pressure is applied to the outer surface of the sheath of the containing vessel to hold the segments of the containing vessel together against internal pressure. The primary hydraulic liquid applied under pressure in the bore of the tubular blank on the one side of the plug can also be applied to the outer surface of the sheath of this form of containing vessel to serve this purpose of holding the segments of the container together against internal pressure.

One embodiment of the invention will now be described by Way of example with reference to the accompanying drawings in which:

FIGURE 1 is a longitudinal sectional elevation,

FIGURE 2 is a cross section along the line II-\II in FIGURE 1.

In the drawings there is shown apparatus for carrying out the method of the invention comprising a pressure tight cylinder 1 closed at its lower end by a plug 2, which is sealed in the bore of the cylinder 1 by a copper mitre ring #3 and a rubber O ring 4. A tubular containing vessel 5 within the cylinder 1 is made up of short longitudinal segments 6 which, as shown in FIGURE 2, have mating radial faces 7. The segments 6 are joined longitudinally by a copper sleeve 8 and are held together radially and sealed by an outer rubber sheath 9, and an annular end plate 10.

In carrying out the method of the invention a tubular blank is fitted in the containing vessel 5, the tubular blank 11 having an end flange 12 which engages with the end of the containing vessel 5. A spherical plug 13 of larger diameter than the original bore diameter D of the tubular blank 11 is forced through the bore of the tubular blank 11 by a primary hydraulic liquid 14 applied under a pressure P in the bore of the tubular blank 10 above the plug 12. The primary hydraulic liquid 14 is pressurised in the cylinder 1 for example by a rain 15 acting in the upper part of the cylinder 1. The hydraulic liquid 14 therefore acts on the outer surface of the rubber sheath 9 of the containing vessel 5 as well as in the bore of the tubular blank 10 above the plug 13. The pressure P of the hydraulic liquid 14 on the outer surface of the rubber sheath 9 of the containing vessel 5 acts to hold the segments 6 of the containing vessel 5 together. Alternatively the hydraulic liquid 14 may be applied only in the bore of the tubular blank 10 above the plug 13 and hydraulic liquid from a separate source may be applied to the outer surface of the rubber sheath 9 of the vessel 5. The hydraulic liquid thus applied separately to the outer surface of the rubber sheath 9 can be applied up to the maximum internal pressure which the cylinder 1 can withstand. In this case the pressure P which can be applied in the hydraulic liquid 14 above the plug 13 is higher than is the case when the hydraulic liquid 14 is also applied on the outer surface of the rubber sheath 9 of the vessel 5. A secondary hydraulic liquid 16 under pressure P is also applied in the bore of the tubular blank 10 below the plug 13. The pressure P in the hydraulic liquid 16 is lower than the pressure P in the hydraulic liquid 14.

Several passes using a series of plugs 13 of gradually increasing diameter may be required to produce a tube of required dimensions from the original tubular blank 11.

With the right combination of liquid pressures P and P above and below the plug 13 tensile stresses in the 3 thinned wall of the tubular blank 11 above the plug 13 can be avoided and in fact the whole process can be carried out with compressive forces existing throughout the tubular blank 11 so that brittle materials can be worked by the method.

The following example relates to the production of a molybdenum tube of 1.000 inch outside diameter and 0.906 inch bore diameter from a tubular blank having the finished outside diameter of 1.000 inch and an original bore diameter of 0.125 inch.

Pressure P1 Pressure P2 Diameter Percent in hydraulic in hydraulic Pass oi plug 13 reduction on liquid 14 liquid 16 pass above plug 13, below plug 13,

tons/in. tons/in.

Reduction in area Original area It is also visualised that if the containing vessel has longitudinal grooves along its bore, longitudinal fins may be formed on the tube produced. Several passes would not affect this situation. This is because the material of the tubular blank moves longitudinally relative to the vessel 5 during each pass of the plug 13 and the material, during deformation into the longitudinal grooves in the bore of the containing vessel 5 to form the fins, will move in the same way. However if the forming operation can be carried out in a single pass, and here softer more readily formable materials might benefit, transverse fins or other more complicated shapes, such as spigots or embossings, can be formed on the outside of the tube.

The containing vessel 5 being of segmented form has the advantage of being easily removable from the tube when formed.

I claim:

1. Apparatus for the production of a thin walled tube by forcing a plug through the bore of a tubular blank, the plug being of larger diameter than the bore of the tubular blank comprising a pressure resistant containing vessel corresponding in internal diameter to the external diameter of the tubular blank, means for generating pressure in a primary hydraulic liquid in the bore of the tubular blank on one side of the plug when entered into the bore of the tubular blank and means for generating a lower pressure in a secondary hydraulic liquid on the other side of the plug in the bore of the tubular blank.

2. Apparatus as claimed in claim 1 wherein the containing vessel for the tubular blank is of cylindrical tubular form comprising longitudinal segments having radial mating faces, the segments being contained within a thin outer sheath, means sealing the end faces of the segments against ingress of hydraulic liquid between the radial mating faces of the segments and means for generating pressure in a hydraulic liquid applied to the outer sheath of the containing vessel to hold the segments of the containing vessel together against internal pressure.

3. Apparatus as claimed in claim 1 wherein the containing vessel for the tubular blank is of cylindrical tubular form comprising longitudinal segments having radial mating faces, the segments being contained within a thin outer sheath, means sealing the end faces of the segments against ingress of hydraulic liquid between the radial mating faces of the segments and means whereby the primary hydraulic liquid applied under pressure in the bore of the tubular blank on the one side of the plug is also applied to the outer surface of the sheath of the containing vessel to hold the segments of the containing vessel together against internal pressure.

4. Apparatus as claimed in claim 1 wherein the internal surface of the containing vessel is formed with recesses so that as the plug is forced through the tubular blank the thin walled tube thus produced is formed with projections on its external surface corresponding to the recesses in the internal surface of the containing vessel.

5. Apparatus as claimed in claim 2 wherein the internal surface of the containing vessel is formed with recesses so that as the plug is forced through the tubular blank the thin walled tube thus produced is formed with projections on its external surface corresponding to the recesses in the internal surface of the containing vessel.

6. Apparatus as claimed in claim 3 wherein the internal surface of the containing vessel is formed with recesses so that as the plug is forced through the tubular blank the thin walled tube thus produced is formed with projections on its external surface corresponding to the recesses in the internal surface of the containing vessel.

References Cited UNITED STATES PATENTS RICHARD J. HERBST, Primary Examiner.

US. Cl. X.R. 

